An image format plugin can support three capabilities: reading (CanRead), writing (CanWrite) and incremental reading (CanReadIncremental). Reimplement capabilities() in you subclass to expose the capabilities of your image format.

create() should create an instance of your QImageIOHandler subclass, with the provided device and format properly set, and return this handler.

The json metadata file for the plugin needs to contain information about the image formats the plugins supports, together with the corresponding MIME types (one for each format). For a jpeg plugin, this could, for example, look as follows:

{
"Keys": ["jpg","jpeg"],"MimeTypes": ["image/jpeg","image/jpeg"]
}

Different plugins can support different capabilities. For example, you may have one plugin that supports reading the GIF format, and another that supports writing. Qt will select the correct plugin for the job, depending on the return value of capabilities(). If several plugins support the same capability, Qt will select one arbitrarily.

Returns the capabilities of the plugin, based on the data in device and the format format. If device is 0, it should simply report whether the format can be read or written. Otherwise, it should attempt to determine whether the given format (or any format supported by the plugin if format is empty) can be read from or written to device. It should do this without changing the state of device (typically by using QIODevice::peek()).

For example, if the QImageIOPlugin supports the BMP format, format is either empty or "bmp", and the data in the device starts with the characters "BM", this function should return CanRead. If format is "bmp", device is 0 and the handler supports both reading and writing, this function should return CanRead | CanWrite.

Creates and returns a QImageIOHandler subclass, with device and format set. The format must come from the values listed in the "Keys" entry in the plugin metadata, or be empty. If it is empty, the data in device must have been recognized by the capabilities() method (with a likewise empty format).